Preparation of Al2TiO5 from alkoxides and the effects of additives on its properties

Al2TiO5 was prepared by the sol-gel method from alkoxides and its mechanical and thermal properties measured. The prepared Al2TiO5 powder was very fine and had a narrow particle-size distribution. The addition of mullite and Al2O3 to the prepared Al2TiO5 inhibited the grain growth during sintering, resulting in a decrease of microcracking and an increase of fracture strength. Al2TiO5/mullite composite exhibited a higher fracture strength than Al2TiO5/alumina composite. The thermal expansion coefficient of Al2TiO5 increased with the addition of mullite and alumina, and also increased with temperature up to 1000°C; however, it decreased in the temperature range between 1000 and 1200°C during heating, due to decomposition of Al2TiO5. The addition of mullite inhibited the decomposition of Al2TiO5, but the addition of Al2O3 accelerated it. Al2TiO5 prepared from metal alkoxides was also more stable than that prepared from the commercial alumina and titania powders. This revised version was published online in November 2006 with corrections to the Cover Date.     

A general SFN structure with transmit diversity for TDS-OFDM system

In the digital television terrestrial broadcasting, the Single Frequency Network (SFN) has much advantage. SFN can serve an arbitrary large area with the same information broadcasted at the same frequency, resulting in the potential diversity gain. To improve the transmission performance of the Time Domain Synchronous-Orthogonal Frequency Division Multiplexing (TDS-OFDM) system in SFN, a general SFN structure with transmit diversity is introduced, theoretically analyzed and computer simulated. The proposed SFN structure is flexible to set up. Simulations show that this method can greatly improve the reliability of the signal transmission over the frequency selective fading channels and is suitable for the TDS-OFDM system in SFN.     

Development of an improved soya protein-lipid film

Soya protein-lipid film, an oriental food material, as traditionally prepared is limited in methionine and has inferior physical properties. A simple modification to the traditional method of preparation, involving addition of DL-methionine and glycerol to soya milk before film formation, yielded a product which was nutritionally improved and obviated the need to reconstitute it.     

在管式填充床反应器中甲醇部分氧化蒸汽重整制氢的模拟研究

Hydrogen production by partial oxidation steam reforming of methanol over a Cu/ZnO/Al2O3 cata-lyst has been paid more and more attention. The chemical equilibria involved in the methanol pvxtial oxidation steam reforming reaction network such as methanol partial oxidation, methanol steam reforming, decomposition of methanol and water-gas shift reaction have been examined over the ranges of temperature 473---1073 K under normal pressure. Based on the detailed kinetics of these reactions over a Cu/ZnO/Al2O3 catalyst, and from the basic concept of the effectiveness factor, the intraparticle diffusion limitations were taken into account. The effectiveness factors for each reaction along the bed length were calculated. Then important results were offered for the simulation of this reaction process.     

Novel zero-voltage and zero-current-switching full bridge PWMconverter using transformer auxiliary winding

A novel zero voltage and zero current switching (ZVZCS) full bridge (FB) pulse width modulation (PWM) converter is proposed to improve the demerits of the previously presented ZVZCS-FB-PWM converters, such as use of lossy components or additional active switches. A simple auxiliary circuit which includes neither lossy components nor active switches provides ZVZCS conditions to primary switches, ZVS for leading-leg switches and ZCS for lagging-leg switches. Many advantages including simple circuit topology, high efficiency, and low cost make the new converter attractive for high power (>2 kW) applications. The operation, analysis, features and design considerations are illustrated and verified on a 2.5 kW, 100 kHz insulated gate bipolar transistor (IGBT) based experimental circuit     

Effect of oxide species and thermomechanical treatments on the strength properties of mechanically alloyed Fe-17%Cr ferritic ODS materials

The effects of several oxide species, such as Y₂0₃, Zr0₂ and MgO, and the thermomechanical treatment (TMT) after the mechanical alloying (MA) process on the strength properties of Fe-17%Cr ferritic ODS (oxide dispersion strengthening) MA materials were investigated. Y20, showed the most uniform dispersion of the finest particles among me above oxides, but the microstructural evolution during the TMT had a larger effect on the strengthening of the alloys than the fine and uniform dispersion of the Y₂O₃ particles had.     

Effects of calcium impurity on phase relationship,ionic conductivity and microstructure of Na<Superscript>+</Superscript>- β / β<Superscript>″</Superscript>-alumina solid electrolyte

Ca-doped Na⁺- β/β^′′-alumina was synthesized using a solid-state reaction. The changes in the properties of Na⁺- β/β^′′-alumina resulting from the presence of Ca impurity were studied. Ca (0–5 wt%) was added to the respective samples, which were then sintered. The specimens were characterized using X-ray diffraction, scanning electron microscopy, densimetry and impedance analysis. In the sintered specimens, the β^′′-alumina phase fraction decreased as Ca content increased, whereas the relative sintered density increased. The surface morphology of Ca-doped Na⁺- β/β^′′-alumina specimens showed a Ca-rich layer, which was the main cause of increase in the specific resistance.     

Transverse vibration of pre-tensioned nonlocal nanobeams with precise internal axial loads

This paper investigates the transverse vibration of a simply supported nanobeam with an initial axial tension based on the nonlocal stress field theory with a nonlocal size parameter. Considering an axial elongation due to transverse vibration, the internal axial tension is not precisely equal to the external initial tension. A sixth-order nonlinear partial differential equation that governs the transverse vibration for such nonlocal nanobeam is derived. Using a perturbation method, the relation between nat...     

X-ray microdiffraction from α-Ti0.04Fe1.96O3 (0001) epitaxial film grown over α-Cr2O3 buffer layer boundary

Ti-doped hematite (α-Ti_0.04Fe_1.96O₃) film grown over patterned α-Cr₂O₃ buffer layer on α-Al₂O₃(0001) substrate was characterized with synchrotron X-ray microdiffraction. The film was grown by oxygen plasma assisted molecular beam epitaxy method. The film growth mode was correlated to buffer layer boundary and Ti concentration variation. Epitaxial α-Ti_0.04Fe_1.96O₃ film was formed on bare substrate adjacent to the buffer layer. The epitaxial film was connected laterally to a strain-relaxed epitaxial α-Ti_0.04Fe_1.96O₃ film grown on the buffer layer. On bare α-Al₂O₃ substrate with diminished Ti concentration only a small portion of α-Ti_xFe_1 − xO₃ film was epitaxial either as coherent to the substrate or strain-relaxed form.